I think it depends on the duration of your workouts ATM. If you’re doing hour long runs, then you can simply take that run to the treadmill or track and perform your workout. After, go into TP and evaluate the drift. If you’re seeing HR rift start getting down to <3%, I would feel comfortable starting to increase my AeT by 2-3 beats.
If you’re not doing hour long runs or you hate the track/treadmill, then I’d stick to the plan and perform a focused HR drift test no quicker than 8 weeks apart. That’s enough time for you to start seeing noticeable improvements if you’re sticking to the plan.
Hopefully a coach will chime in if they have anything to add/correct!